Conventional support and track systems for vertical blinds and roller shades have concentrated on two problems with two different structures.
First, for vertical blinds, the main objective has been to eliminate friction in actuating the rotation of the control rod which extends along the drapery track and which turns the individual vertical blind units simultaneously to admit or shut off light from entering the room. The control rod engages a gear associated with each support structure for each vertical blind panel, known as a carrier. The carrier has the ability to freely translate and roll within a raceway within the track, the system then having an ability to rotate the control rod to change the angle of the vertical blind panels regardless of where the carriers are located along the track.
Thus, the rod's contact with several carriers adds significant mechanical resistance to turning, especially when the turning is accomplished from the end of the vertical blind track. A significant turning force complicates the actuation with a pull chain, as the pull chain sprocket will normally experience additional friction from being actuated by being pulled downward, at a right angle from its axis of rotation.
One method and technique which has been applied to this problem is the use of the concentric reducing gear. This normally cuts the pull chain force in half by doubling the length of travel of the pull chain, but because of the lateral force friction, probably reduces the force by about 1/3. This can make the operation of the vertical blind set fussy and time consuming. Moreover, the gear mechanism significantly increases the cost of the mechanism, both from a number of parts standpoint, assembly standpoint, and even more importantly from a tolerance standpoint.
The cost for injection molded parts increases significantly once the tolerance specifications are made more exacting. Where several parts have to fit together and work properly, the tolerances have to be controlled within strict limits. Stricter limits translate to longer cycle times in the injection mold process and greater waste, both of which drive up the cost.
The size factor multiplies and exacerbates the above factors. Keeping tolerance on a small part is difficult. Having a series of smaller parts perform a load bearing function doesn't leave much room for wear. The use of a metal ball bearing set is out of the question as the added cost would be unbearable by the market.
Roller shades present the problem of controlled friction, coupled with bearing lateral force resistance and wear. One popular design uses a two ended coil spring which is activated by pushing the spring in an unwind direction to cause it to lose its grip and move. The spring, however, produces a good deal of friction upon the cylindrical tube upon which it is mounted. So, where the spring is made strong enough to strongly resist pulling on the window shade, it adds significant friction to the tube upon which it is mounted. Since the ends of the springs are all that hold the window shade in place, making a smaller spring would cause the force from the shade to bend the spring ends. As a result, the window covering industry has had to settle for a device which produces significant resistance to operation in order to provide window roller shade control. In reality, the force moment on a roller shade is small due to a general balance of material when rolled up, and a relatively short turning moment when fully unrolled.
In both the window shade and vertical blind configurations, the necessity to place greater force on the actuating member, particularly in the downward direction, means that greater time and effort must be expended in making certain that the mounting of the track or bracket is sufficient to withstand the pulling force of the actuation member, usually a looping suspended chain. So even in instances where dry wall would be sufficient to hold the roller shade or vertical blinds and more, additional labor and structure will be needed to further anchor the window covering device to a stud or beam. Of course, all installations should be secure, but where additional anchoring is needed simply because of the unreasonable forces needed to operate the window covering mechanism, the added money for much higher installation costs are not justified.
What is therefore needed is a mechanism for a window covering device which can be inexpensively injection molded and which makes up for relaxed tolerance in manufacture. The device should have load bearing capability and for roller shades, the resistive force to prevent the unwinding of the window shade should be adjustable.